I have decided it is a girl. Last night, I worked late. After work, I saw two young girls and one young boy (I'm very bad with guessing ages, but I'd say all between 9 - 11 years old) outside. I know each of them by name, they live around here and we sometimes see one another, and they play outside my window after school.
I was about to get into my car and drive home, when I thought, who better to ask than the generation the letter came from. So I approached the young boy and two girls, said hi, and asked "do you think the name Shelby is a boy or a girl?" Which of course got them to thinking, why is a grown-up asking us this, which means I had to tell them the whole story. The little girl in the ballet outfit and tutu said to me, "Do you have the letter with you?" and I said yes, and she informed me that girls' and boys' handwriting looks different.
All three children carefully read out loud and examined the letter. The handwriting was "neat" and therefore decided by the children to be a girl's handwriting.
The experts have voted!!!